1. Field of the Invention
The present invention relates to a weight and form sensing apparatus and a packaging machine using the same.
2. Description of the Prior Art
An automatic packaging machine, which puts an article such as foods on a tray and packaging the article with a film by packaging operation such as stretching and shrinking the film, is commonly utilized. The packaging machine being able to package the article according to weight and size of the article, so-called stretch packaging machine, is also utilized.
One example for an automatic packaging process of the stretch packaging machine is described below. First, the article, e.g. food with the tray, is put on a conveyance unit of the machine. The article is weighed at the conveyance unit by a balance such as a load cell balance. The article is conveyed to a packaging unit by a conveyance mechanism such as a belt conveyer. The size (height and length) of the tray is measured by sensors such as optical sensors while the article is conveyed. The film having suitable width is selected as to the measured size of the article, selected film is drawn out from a film supply unit with certain amount, a film clamping mechanism clamps the drawn film and stretches the film in width direction of the film, so that the stretch packaging machine waits for packaging operation.
When the article is positioned under the film in the packaging unit, the stretch packaging unit conveys the article upwardly to the waiting film by a lifter. Then,the packaging operation begins when the article touched the film so as to package the article with the film. The packaged article is conveyed towards an outlet. A label, printed necessary matters such as the weight, name of the article and price of the article, is adhered to the article by a labeling machine while the end of the film is melted and curing.
The disadvantage of the above conventional stretch packaging machine is now described. The weight of the article is detected by the balance such as the load cell balance. The size of the article, i.e., the tray, is measured by sensors such as reflect type optical sensors or transmission type optical sensors disposed under a conveyance belt or sides of the conveyance belt in constant interval while the article is conveyed. These sensors should be disposed at places which do not interfere with the conveyance mechanism.
Accordingly, different sensing mechanisms are required for weighing and measuring the article, so that a number or parts for sensing weight and form of the article is large and the mechanism becomes complicated. Also, the sensors for measuring the size of the article should be disposed at the places not interfering with the conveyance mechanism, so that the arrangement of the sensors are limited.
Accordingly, it is an object of the present invention to be capable of sensing the weight and size of the article with single sensing mechanism.
Another object of the present invention is to provide simple structure for sensing the weight and size of the article.
A further object of the present invention is to eliminate the arrangement for preventing the interference between the sensing mechanism and the conveyance mechanism.
A further object of the present invention is to improve the arrangement of each portion.
These and further object of the present invention are achieved by the novel weight and form sensing apparatus having a base, weight sensors each having a load receiving portion on a top and disposed on the base. The novel apparatus according to the present invention sums output value of each weight sensor, so that an article put on the weight sensors is weighed. The novel apparatus according to the present invention also determines existence of the load on each weight sensor based on output signal of each weight sensor, so that the form and size of the article are identified.
According to the novel packaging machine of the present invention includes a weight and form sensing apparatus comprises a base and weight sensors each having a load receiving portion on a top and disposed on the base. The novel machine according to the present invention sums output value of each weight sensor, so that an article put on the weight sensors is weighed. The novel machine according to the present invention also determines existence of the load on each weight sensor based on output signal of each weight sensor, so that the form and size of the article are identified Then, the article is packaged in a tray with a film after weight and form of the article are sensed by the weight and form sensing apparatus.